Serial Port And Usb Interface; Function Of Serial Port - SimCom SIM800L Hardware Design

Note: The clock error becomes larger when VBAT is turned off and RTC circuit was supplied from the backup battery or the
external capacitor.

4.5. Serial Port and USB Interface

SIM800L default provides one unbalanced asynchronous serial ports. The module is designed as a DCE (Data
Communication Equipment). The following figure shows the connection between module and client (DTE).
Table 9: Serial port and USB pin definition
Pin name
DTR
RI
DCD
Serial port CTS
RTS
TXD
RXD
VBUS
Debug port USB_DP
USB_DN
Note: Hardware flow control is disable by default. AT command "AT+IFC=2,2"can enable hardware flow control. AT command
"AT+IFC=0,0"can disable hardware flow control. For more details please refer to document [1].
Table 10: Serial port characteristics
Symbol
V
IL
V
IH
V
OL
V
OH
4.5.1

Function of Serial Port

Serial port:
Full mode device.

Contains data lines TXD and RXD, hardware flow control lines RTS and CTS, status lines DTR, DCD and

RI.
Serial port can be used for CSD FAX, GPRS service and AT communication. It can also be used for

multiplexing function. For details about multiplexing function, please refer to table 11.
Serial port supports the following baud rates:

1200, 2400, 4800, 9600, 19200, 38400, 57600,115200,230400 and 460800bps
Autobauding only supports the following baud rates:

1200, 2400, 4800, 9600, 19200, 38400, 57600 and 115200bps
SIM800L(MT6261)_Hardware Design_V1.01
Pin number Function
69 Data terminal ready
68 Ring indicator
70 Data carrier detect
34 Request to send
33 Clear to send
32 Transmit data
31 Receive data
7 USB power supply
59 USB data line positive
19 USB data line negative
Min Typ
-0.3 -
2.1 -
- -
2.4 2.8
Smart Machine Smart Decision
Max
0.7
3.1
0.4
-
28
Unit
V
V
V
V
2016-07-07